Inorganic solvent systems for lanthanide ions

Abstract

Lanthanide ions dissolved in low vibrational frequency inorganic liquids have potential applications in laser systems requiring long non radiative lifetimes such as mid infrared and up conversion lasers. The use of liquids, whilst presenting some thermal and technological problems, avoids costly crystal growth and fabrication and gives great flexibility in varying lanthanide species, doping levels and co-doping. We report an extensive study of solvent systems based on POCl 3, PSCl 3, PBr 3, PCl 3, AsCl 3, SbCl 3 and SbBr 3. The relatively well known POCl 3 system is found to show a far more complex behaviour than the early literature suggests because of formation of the adduct 2POCl 3:SnCl 4. The other species except for PBr 3 and PCl 3 prove unsuitable owing to the ready production of absorbing species. PBr 3 and PCl 3 produce solvent systems when combined with the Lewis acids AlBr 3 and SbBr 3 or AlCl 3 and SbCl 3 respectively. The energy levels of all laser relevant lanthanide ions below ∼ 20 000 cm −1 were determined in the PBr 3 solvent system, and correlations between the required Lewis acid concentration and the lanthanide element found. Comparison of the spectra in various solvents leads to preliminary conclusions about the lanthanide ion coordination.